The National Weather Service said a warming brought by a strong, upper-level high centered over the Great Basin would peak on today and Wednesday. Excessive heat warnings will be in effect most of Tuesday across the deserts, the NWS said.

AccuWeather forecasts 103 Tuesday and Wednesday for Victorville, as well as 100 on Thursday.

Residents are urged to take precautions that will prevent heat-related illness.

Extremely high or unusually hot temperatures can affect your health. Most vulnerable are the elderly, those who work or exercise outdoors, infants and children, the homeless or poor, and people with a chronic medical condition.

Forecasters also warned that the heat, combined with low humidity levels, will elevate the fire danger. Firefighters jumped on several small fires Monday in San Bernardino, San Diego and Los Angeles counties.

Dry lightning will add to fire worries as a flow of monsoonal moisture arrives from the southeast later in the week, affecting Southern California and the southern Sierra Nevada, the NWS said.

Residents are advised to the necessary precautions to prevent serious health effects such as heat exhaustion or heat stroke.

Stay cool

• Stay in air-conditioned buildings.

• Find an air-conditioned Cooling Center open to the public by dialing the United Way's toll-free resource telephone line at 2-1-1, or online at www.coolingsb.org.

• Do not rely on a fan as your primary cooling device.

• Limit outdoor activity, especially midday when it is the hottest part of the day, and avoid direct sunlight.

• Wear loose, lightweight, light-colored clothing.

• Take cool showers or baths to lower your body temperature.

• Check on at-risk friends, family and neighbors at least twice a day.

Stay hydrated

• Drink more than usual and don't wait until you're thirsty to drink.

• Drink from two to four cups of water every hour while working or exercising outside.

Additionally, the San Bernardino County Department of Public Health encourages all residents to learn the signs and first aid response for heat-related illness. Warning signs and symptoms vary but may include:

Heat exhaustion symptoms include:

• Heavy sweating

• Weakness

• Skin cold, pale, and clammy

• Weak pulse

• Fainting and vomiting

What you should do:

• Move to a cooler location

• Lie down and loosen your clothing

• Apply cool, wet clothes to as much of your body as possible

• Sip water

• If you have vomited and if it continues, seek medical attention immediately

Heat stroke symptoms:

• High body temperature (above 103 degrees)

• Hot, red, dry or moist skin

• Rapid and strong pulse

• Possible unconsciousness

What you should do:

• Call 911 immediately — this is a medial emergency

• Move the person to a cooler environment

• Reduce the person's body temperature with cool clothes or even a bath

• Do not give fluids

For more information on extreme heat, call the San Bernardino County Department of Public Health at (800) 782-4264, or the United Way's San Bernardino County toll-free resource telephone line by dialing 211, or visit the California Department of Public Health website at: http://www.bepreparedcalifornia.ca.gov/BeInformed/NaturalDisasters/ExtremeHeat/Pages/Extreme+Heat.aspx

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